Plasma etching method for selectively etching silicon oxide with respect to silicon nitride

ABSTRACT

An etching method is provided for selectively etching a first region of silicon oxide with respect to a second region of silicon nitride by performing plasma processing on a target object including the first region and the second region. In the etch method, first, a plasma of a processing gas including a fluorocarbon gas is generated in a processing chamber where the target object is accommodated. Next, the plasma of the processing gas including the fluorocarbon gas is further generated in the processing chamber where the target object is accommodated. Next, the first region is etched by radicals of fluorocarbon contained in a deposit which is formed on the target object by the generation and the further generation of the plasma of the processing gas containing the fluorocarbon gas. A high frequency powers used for the plasma generation is smaller than a high frequency power used for plasma further generation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/112,435, filed Aug. 24, 2018 which is a continuation of U.S. patentapplication Ser. No. 14/995,552, filed Jan. 14, 2016, now U.S. Pat. No.10,109,495, and claims priority to Japanese Patent Application No.2015-006771, filed Jan. 16, 2015, the disclosures of which areincorporated herein in their entirety by reference, and priority isclaimed to each of the foregoing.

FIELD OF THE INVENTION

The disclosure relates to an etching method, and more particularly, to amethod for selectively etching a first region of silicon oxide withrespect to a second region of silicon nitride by performing plasmaprocessing on a target object.

BACKGROUND OF THE INVENTION

In manufacturing electronic devices, there is performed a process offorming an opening such as a hole or a trench at a region of siliconoxide (SiO₂). In such a process, a target object is exposed to a plasmaof a fluorocarbon gas and then, the region of silicon oxide is etched,as disclosed in U.S. Pat. No. 7,708,859.

There is known a technique for selectively etching a first region ofsilicon oxide with respect to a second region of silicon nitride. A SAC(Self-Aligned Contact) technique disclosed in Japanese PatentApplication Publication No. 2000-307001 is known as an example of such atechnique.

The target object to be processed by the SAC technique includes a firstregion of silicon oxide, a second region of silicon nitride, and a mask.The second region is formed to have a recess. The first region is formedto fill the recess and cover the second region. The mask is provided onthe first region and has an opening provided over the recess. Asdisclosed in Japanese Patent Application Publication No. 2000-307001, inthe conventional SAC technique, a plasma of a processing gas including afluorocarbon gas, an oxygen gas and a rare gas is used to etch the firstregion. By exposing the target object to the plasma of the processinggas, a portion of the first region which is exposed through the openingof the mask is etched. As a consequence, an upper opening is formed.Further, by exposing the target object to the plasma of the processinggas, a portion surrounded by the second region, i.e., the first regionin the recess, is etched in a self-aligned manner. Accordingly, a loweropening continuous to the upper opening is formed in a self-alignedmanner.

In the above-described conventional technique, at a time when the secondregion is exposed in the course of etching the first region, thereoccurs a state where a film for protecting the second region is notformed on a surface of the second region. Thus, if the etching of thefirst region is further performed in this state, a portion of the secondregion is also etched.

SUMMARY OF THE INVENTION

In view of the above, the disclosure provides an etching method foretching the first region of silicon oxide while suppressing etching ofthe second region of silicon nitride.

In accordance with an aspect of the disclosure, there is provided anetching method for selectively etching a first region of silicon oxidewith respect to a second region of silicon nitride by performing plasmaprocessing on a target object including the first region and the secondregion. In the etch method, first, a plasma of a processing gasincluding a fluorocarbon gas is generated in a processing chamber wherethe target object is accommodated. Next, the plasma of the processinggas including the fluorocarbon gas is further generated in theprocessing chamber where the target object is accommodated. Next, thefirst region is etched by radicals of fluorocarbon contained in adeposit which is formed on the target object by the generation and thefurther generation of the plasma of the processing gas including thefluorocarbon gas. A high frequency powers used for the plasma generationis smaller than a high frequency power used for plasma furthergeneration.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the disclosure will become apparent from thefollowing description of embodiments, given in conjunction with theaccompanying drawings, in which:

FIG. 1 is a flowchart of an etching method according to an embodiment;

FIG. 2 is a cross sectional view showing an example of a target objectto which the etching method according to the embodiment is applied;

FIG. 3 schematically shows an example of a plasma processing apparatuscapable of performing the method shown in FIG. 1; and

FIGS. 4 to 17 are cross sectional views showing the target object inrespective steps of the etching method shown in FIG. 1.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments will be described with reference to theaccompanying drawings. Like reference numerals will be used for likeparts throughout the drawings.

FIG. 1 is a flowchart of an etching method according to an embodiment. Amethod MT shown in FIG. 1 is an etching method for selectively etching afirst region of silicon oxide with respect to a second region of siliconnitride by performing plasma processing on a target object.

FIG. 2 is a cross sectional view showing an example of a target objectto which the etching method according to the embodiment is applied. Asshown in FIG. 2, the target object, i.e., a wafer W, includes asubstrate SB, a first region R1, a second region R2, and an organic filmOL that will becomes a mask later. For example, this wafer W is obtainedduring the manufacturing process of a fin-type field effect transistorand further includes a protruding region RA, a silicon-containinganti-reflection film AL, and a resist mask RM.

The protruding region RA protrudes from the substrate SB. The protrudingregion RA may serve as, e.g., a gate region. The second region R2 ismade of silicon nitride (Si₃N₄) and formed on surfaces of the protrudingregion RA and the substrate SB. As shown in FIG. 2, the second region R2extends to form a recess. For example, the recess has a depth of about150 nm and a width of about 20 nm.

The first region R1 is made of silicon oxide (SiO₂) and formed on thesecond region R2. Specifically, the first region R1 fills the recessformed by the second region R2 and covers the second region R2.

The organic film OL is formed on the first region R1. The organic filmOL may be made of an organic material, e.g., amorphous carbon. Theanti-reflection film AL is formed on the organic film OL. The resistmask RM is formed on the anti-reflection film AL. The resist mask RMprovides an opening having a width greater than that of the recessformed by the second region R2. The opening of the resist mask RM has awidth of, e.g., about 60 nm. A pattern of the resist mask RM is formedby a photolithography technique.

In the method MT, the target object such as the wafer W shown in FIG. 2is processed in a plasma processing apparatus. FIG. 3 schematicallyshows an example of a plasma processing apparatus capable of performingthe method shown in FIG. 1. A plasma processing apparatus 10 shown inFIG. 3 is configured as a capacitively coupled plasma etching apparatusand includes a substantially cylindrical processing chamber 12. An innerwall surface of the processing chamber 12 is made of, e.g., anodizedaluminum. The processing chamber 12 is frame-grounded.

A substantially cylindrical supporting part 14 is provided at a bottomportion of the processing chamber 12. The supporting part 14 is made of,e.g., an insulating material. In the processing chamber 12, thesupporting part 14 extends vertically from the bottom portion of theprocessing chamber 12. Further, in the processing chamber 12, a mountingtable PD is provided. The mounting table PD is supported by thesupporting part 14.

The wafer W is held on a top surface of the mounting table PD. Themounting table PD includes a lower electrode LE and an electrostaticchuck ESC. The lower electrode LE has a first plate 18 a and a secondplate 18 b. The first plate 18 a and the second plate 18 b are made of ametal, e.g., aluminum, and have a substantially disc shape. The secondplate 18 b is provided on the first plate 18 a and electricallyconnected to the first plate 18 a.

An electrostatic chuck ESC is provided on the second plate 18 b. Theelectrostatic chuck ESC has a structure in which an electrode made of aconductive film is interposed between two insulating layers or twoinsulating sheets. A DC power supply 22 is electrically connected to theelectrode of the electrostatic chuck ESC through a switch 23. The waferW is attracted and held on the electrostatic chuck ESC by anelectrostatic force such as a Coulomb force or the like generated by aDC voltage applied from the DC power supply 22.

A focus ring FR is provided on a peripheral portion of the second plate18 b to surround an edge of the wafer W and the electrostatic chuck ESC.The focus ring FR is provided to improve uniformity of etching. Thefocus ring FR is made of a material that is appropriately selecteddepending on a material of an etching target film. For example, thefocus ring FR may be made of quartz.

A coolant path 24 is provided in the second plate 18 b. The coolant path24 constitutes a temperature control mechanism. A coolant is supplied tothe coolant path 24 from an external chiller unit through a line 26 a.The coolant flowing in the coolant path 24 returns to the chiller unitthrough a line 26 b. The coolant circulates between the coolant path 24and the chiller unit. A temperature of the wafer W held on theelectrostatic chuck ESC is controlled by controlling a temperature ofthe coolant.

The plasma processing apparatus 10 further includes a gas supply line28. A heat transfer gas supply unit (not shown) supplies a heat transfergas, e.g., He gas to a gap between a top surface of the electrostaticchuck ESC and a backside of the wafer W through the gas supply line 28.

The plasma processing apparatus 10 further includes an upper electrode30. The upper electrode 30 is provided above the mounting table PD toface the mounting table PD. The upper electrode 30 and the lowerelectrode LE are approximately parallel to each other. Between the upperelectrode 30 and the lower electrode LE, a processing space S whereplasma processing is performed on the wafer W is defined.

The upper electrode 30 is held at an upper portion of the processingchamber 12 through an insulating shield member 32. In the presentembodiment, the upper electrode 30 may be configured such that avertical distance from a top surface of the mounting table PD, i.e., awafer mounting surface, to the upper electrode 30 is variable. The upperelectrode 30 may include an electrode plate 34 and an electrode plateholder 36. The electrode plate 34 is in contact with the space S and hasa plurality of gas injection openings 34 a. In the present embodiment,the electrode plate 34 is made of silicon.

The electrode plate holder 36 detachably holds the electrode plate 34and is made of a conductive material, e.g., aluminum. The electrodeplate holder 36 may have a water cooling structure. A gas diffusionspace 36 a is provided in the electrode plate holder 36. A plurality ofgas passage holes 36 b communicating with the gas injection openings 34a extends downward from the gas diffusion space 36 a. Further, theelectrode plate holder 36 includes a gas inlet port 36 c for guiding aprocessing gas into the gas diffusion space 36 a. A gas supply line 38is connected to the gas inlet port 36 c.

The gas supply line 38 is connected to a gas source group 40 through avalve group 42 and a flow rate controller group 44. The gas source group40 includes a plurality of gas sources. In this example, the gas sourcegroup 40 includes one or more fluorocarbon gas sources, a rare gassource, a nitrogen gas (N₂ gas) source, a hydrogen gas (H₂ gas) source,and an oxygen-containing gas source. One or more fluorocarbon gassources may include a C₄F₈ gas source, a CF₄ gas source, and a C₄F₆ gassource. The rare gas source may be a source of any rare gas such as Hegas, Ne gas, Ar gas, Kr gas, Xe gas or the like. In this example, therare gas source may be an Ar gas source. In this example, theoxygen-containing gas source may be an oxygen gas (O₂ gas) source. Theoxygen-containing gas may also be any gas containing oxygen, e.g., acarbon oxide gas such as CO gas or CO₂ gas.

The valve group 42 includes a plurality of valves. The flow ratecontroller group 44 includes a plurality of flow rate controllers suchas a mass flow rate controller and the like. The gas sources of the gassource group 40 are connected to the gas supply line 38 throughcorresponding valves of the valve group 42 and corresponding flow ratecontrollers of the flow rate controller group 44, respectively.

In the plasma processing apparatus 10, a deposition shield 46 isdetachably provided along the inner wall of the processing chamber 12.The deposition shield 46 is also provided at an outer periphery of thesupporting part 14. The deposition shield 46 prevents an etchingby-product (deposit) from being adhered to the processing chamber 12.The deposition shield 46 may be made of aluminum coated with ceramicsuch as Y₂O₃ or the like.

A gas exhaust plate 48 is provided at a lower portion in the processingchamber 12 and between the supporting part 14 and the sidewall of theprocessing chamber 12. The gas exhaust plate 48 may be formed by coatingaluminum with ceramic, e.g., Y₂O₃ or the like. In the processing chamber12, a gas exhaust port 12 e is provided below the gas exhaust plate 48.A gas exhaust unit 50 is connected to the gas exhaust port 12 e througha gas exhaust line 52. The gas exhaust unit 50 has a vacuum pump such asa turbo molecular pump or the like, and can depressurize the space inthe processing chamber 12 to a predetermined vacuum level. Aloading/unloading port 12 g for the wafer W is provided at the sidewallof the processing chamber 12. The loading/unloading port 12 g can beopened and closed by a gate valve 54.

The plasma processing apparatus 10 further includes a first highfrequency power supply 62 and a second high frequency power supply 64.The first high frequency power supply 62 generates a high frequencypower for plasma generation, e.g., a high frequency power having afrequency in a range from 27 MHz to 100 MHz. The first high frequencypower supply 62 is connected to the upper electrode 30 through amatching unit 66. The matching unit 66 is a circuit for matching anoutput impedance of the first high frequency power supply 62 with aninput impedance of the load side (the upper electrode 30 side). Thefirst high frequency power supply 62 may be connected to the lowerelectrode LE through the matching unit 66.

The second high frequency power supply 64 generates a high frequencybias power for ion attraction to the wafer W, e.g., a high frequencybias power having a frequency in a range from 400 kHz to 13.56 MHz. Thesecond high frequency power supply 64 is connected to the lowerelectrode LE through a matching unit 68. The matching unit 68 is acircuit for matching an output impedance of the second high frequencypower supply 64 with an input impedance of the load side (the lowerelectrode LE side).

The plasma processing apparatus 10 further includes a power supply 70.The power supply 70 is connected to the upper electrode 30. The powersupply 70 applies to the upper electrode 30 a voltage for attractingpositive ions in the processing space S to the electrode plate 34. Inthis example, the power supply 70 is a DC power supply for generating anegative DC voltage. In another example, the power supply 70 may be anAC power supply for generating an AC voltage having a relatively lowfrequency. The voltage applied from the power supply 70 to the upperelectrode 30 may be lower than or equal to −150V. In other words, thevoltage applied from the power supply 70 to the upper electrode 30 maybe a negative voltage having an absolute value of 150 or above. Whensuch a voltage is applied from the power supply 70 to the upperelectrode 30, the positive ions in the processing space S collide withthe electrode plate 34. Accordingly, secondary electrons and/or siliconare emitted from the electrode plate 34. The emitted silicon is combinedwith active species of fluorine in the processing space S, so that theamount of active species of fluorine is decreased.

In the present embodiment, the plasma processing apparatus 10 mayfurther include a control unit Cnt. The control unit Cnt is a computerincluding a processor, a storage unit, an input device, a display deviceand the like. The control unit Cnt controls the respective components ofthe plasma processing apparatus 10. The control unit Cnt can allow anoperator to input commands to manage the plasma processing apparatus 10by using the input device and display the operation state of the plasmaprocessing apparatus 10 on the display device. The storage unit of thecontrol unit Cnt stores therein a control program for controllingvarious processes performed in the plasma processing apparatus 10, and aprogram, i.e., a processing recipe, for performing processes of therespective components of the plasma processing apparatus 10 based on theprocessing conditions.

Referring back to FIG. 1, the method MT1 will be described in detail.FIGS. 2 and 4 to 17 will be appropriately referred to in the followingdescription. FIGS. 4 to 17 are cross sectional views showing the targetobject in respective steps of the method MT. In the followingdescription, there will be described an example in which the wafer Wshown in FIG. 2 is processed by the plasma processing apparatus 10 shownin FIG. 3 according to the method MT.

In the method MT, first, the wafer W shown in FIG. 2 is loaded into theplasma processing apparatus 10 and then mounted and held on the mountingtable PD.

Next, a step ST1 of the method MT1 is executed. In the step ST1, theanti-reflection film AL is etched. To do so, a processing gas issupplied into the processing chamber 12 from a gas source selected amongthe gas sources of the gas source group 40. This processing gas used inthe step ST1 includes a fluorocarbon gas. The fluorocarbon gas maycontain, e.g., at least one of C₄F₈ gas and CF₄ gas. The processing gasmay further include a rare gas, e.g., Ar gas. In the step ST1, apressure in the processing chamber 12 is set to a predetermined level bythe operation of the gas exhaust unit 50. In the step ST1, the highfrequency power from the first high frequency power supply 62 and thehigh frequency bias power from the second high frequency power supply 64are supplied to the lower electrode LE.

The step ST1 is executed under the following condition.

Pressure in processing chamber: 10 mTorr (1.33 Pa) to 50 mTorr (6.65 Pa)

Processing Gas

-   -   C₄F₈ gas: 10 sccm to 30 sccm    -   CF₄ gas: 150 sccm to 300 sccm    -   Ar gas: 200 sccm to 500 sccm

High frequency power for plasma generation: 300 W to 1000 W

High frequency bias power: 200 W to 500 W

In the step ST1, the plasma of the processing gas is generated and aportion of the anti-reflection film AL which is exposed through theopening of the resist mask RM is etched by active species offluorocarbon. As a result, the portion of the anti-reflection film ALwhich is exposed through the opening of the resist mask RM is removed ascan be seen from FIG. 4. In other words, a pattern of the resist mask RMis transferred onto the anti-reflection film AL and the anti-reflectionfilm AL is formed to have a pattern providing an opening. In the stepST1, the operation of each component of the plasma processing apparatus10 can be controlled by the control unit Cnt.

Next, in a step ST2, the organic film OL is etched. To do so, aprocessing gas is supplied into the processing chamber 12 from a gassource selected among the gas sources of the gas source group 40. Thisprocessing gas used in the step ST2 may include hydrogen gas andnitrogen gas. Moreover, the processing gas used in the step ST2 maycontain another gas, e.g., oxygen gas, as long as it can etch theorganic film. In the step ST2, a pressure in the processing chamber 12is set to a predetermined level by the operation of the gas exhaust unit50. In the step ST2, the high frequency power from the first highfrequency power supply 62 and the high frequency bias power from thesecond high frequency power supply 64 are supplied to the lowerelectrode LE.

The step ST2 is executed under the following condition.

Pressure in processing chamber: 50 mTorr (6.65 Pa) to 200 mTorr (26.6Pa)

Processing Gas

-   -   N₂ gas: 200 sccm to 400 sccm    -   H₂ gas: 200 sccm to 400 sccm

High frequency power for plasma generation: 500 W to 2000 W

High frequency bias power: 200 W to 500 W

In the step ST2, the plasma of the processing gas is generated and aportion of the organic film OL which is exposed through the opening ofthe anti-reflection film AL is etched. The resist mask RM is alsoetched. As a result, the resist mask RM is removed and the portion ofthe organic film OL which is exposed through the opening of theanti-reflection film AL is removed, as can be seen from FIG. 5. In otherwords, the pattern of the anti-reflection film AL is transferred ontothe organic film OL and the organic film OL is formed to have a patternproviding an opening MO, thereby serving as a mask MK. In the step ST2,the operation of each component of the plasma processing apparatus 10can be controlled by the control unit Cnt.

In the present embodiment, a step ST3 is executed after the step ST2. Inthe step ST3, the first region R1 is etched. The etching of the firstregion R1 is stopped immediately before the second region R2 is exposed.In other words, the first region R1 is etched until the first region R1remains a little on the second region R2. To do so, in the step ST3, aprocessing gas is supplied into the processing chamber 12 from a gassource selected among the gas sources of the gas source group 40. Thisprocessing gas used in the step ST3 includes a fluorocarbon gas.Moreover, the processing gas may further include a rare gas, e.g., Argas. Further, the processing gas may include oxygen gas. In the stepST3, a pressure in the processing chamber 12 is set to a predeterminedlevel by the operation of the gas exhaust unit 50. In the step ST3, thehigh frequency power supply from the first high frequency power supply62 and the high frequency bias power from the second high frequencypower supply 64 are supplied to the lower electrode LE.

In the step ST3, the plasma of the processing gas is generated and aportion of the first region R1 which is exposed through the opening ofthe mask MK is etched by active species of fluorocarbon. The processingtime of the step ST3 is set such that the etched first region R1 havinga predetermined film thickness remains on the second region R2 after theexecution of the step ST3. As a result of the execution of the step ST3,an upper opening UO is partially formed as can be seen from FIG. 6. Theoperation of each component of the plasma processing apparatus 10 in thestep ST3 can be controlled by the control unit Cnt.

In a step ST11 and a step ST12 which will be described later, thecondition that realizes a deposition mode, i.e., a mode in whichdeposition of deposit containing fluorocarbon on the surface of thewafer W including the first region R1 dominates over the etching of thefirst region R1, is selected. On the other hand, in the step ST3, thecondition that realizes an etching mode, i.e., a mode in which theetching of the first region R1 dominates over the deposition of deposit,is selected. To do so, in this example, the fluorocarbon gas used in thestep ST3 may include at least one of C₄F₈ gas and CF₄ gas. A ratio offluorine atoms to carbon atoms (i.e., the number of fluorine atoms/thenumber of carbon atoms) in the fluorocarbon gas used in the step ST3 ishigher than that in the fluorocarbon gas used in the step ST11 and thestep ST12. In this example, in order to increase a degree ofdissociation of the fluorocarbon gas, the high frequency power forplasma generation used in the step ST3 may be set to be greater thanthat used in the step ST11 and the step ST12. Accordingly, the etchingmode can be realized. Moreover, in this example, the high frequency biaspower used in the step ST3 may be set to be greater than the highfrequency bias power used in the step ST11 and the step ST12.Accordingly, the energy of ions attracted to the wafer W can beincreased, so that the first region R1 can be etched at a high speed.

The step ST3 is executed under the following condition.

Pressure in processing chamber: 10 mTorr (1.33 Pa) to 50 mTorr (6.65 Pa)

Processing Gas

-   -   C₄F₈ gas: 10 sccm to 30 sccm    -   CF₄ gas: 50 sccm to 150 sccm    -   Ar gas: 500 sccm to 1000 sccm    -   O₂ gas: 10 sccm to 30 sccm

High frequency power for plasma generation: 500 W to 2000 W

High frequency bias power: 500 W to 2000 W

Next, a step ST4 is executed. In the step ST4, a plasma of a processinggas containing an oxygen-containing gas is generated in the processingchamber 12. To do so the processing gas is supplied into the processingchamber 12 from a gas source selected among the gas sources of the gassource group 40. In this example, this processing gas used in the stepST4 may contain oxygen gas as an oxygen-containing gas. Moreover, theprocessing gas may further include a rare gas (e.g., Ar gas) or an inertgas such as nitrogen gas. In the step ST4, a pressure in the processingchamber 12 is set to a predetermined level by the operation of the gasexhaust unit 50. In the step ST4, the high frequency power from thefirst high frequency power supply 62 is supplied to the lower electrodeLE. In the step ST4, the high frequency bias power from the second highfrequency power supply 64 may not be supplied to the lower electrode LE.

In the step ST4, active species of oxygen are generated. A width of anupper end portion of the opening MO of the mask MK is increased by theactive species of oxygen. Specifically, an upper shoulder portion of themask MK which forms the upper end portion of the opening MO is etched ina tapered shape as can be seen from FIG. 7. Accordingly, even if adeposit generated in the following steps is adhered to a surfacedefining the opening MO of the mask MK, the decrease in the width of theopening MO can be reduced. The operation of each component of the plasmaprocessing apparatus 10 in the step ST4 can be controlled by the controlunit Cnt.

In a step ST13 to be described later, the step ST13 is carried out todecrease a very small amount of deposit generated in each sequence, andthere is a need to suppress excessive decrease of the deposit. On theother hand, the step ST4 is executed to increase the width of the upperend portion of the opening MO of the mask MK and the processing time ofthe step ST4 needs to be short.

The step ST4 is executed under the following condition.

Pressure in processing chamber: 30 mTorr (3.99 Pa) to 200 mTorr (26.6Pa)

Processing Gas

-   -   O₂ gas: 50 sccm to 500 sccm    -   Ar gas: 200 sccm to 1500 sccm

High frequency power for plasma generation: 100 W to 500 W

High frequency bias power: 0 W to 200 W

Next, in the method MT, a sequence SQ is performed to etch the firstregion R1. In the present embodiment, the sequence SQ is repeatedlyperformed. The sequence SQ includes a step ST11, a step ST12, and a stepST14 that are executed in that order. In the present embodiment, thesequence SQ further includes a step ST13 executed between the step ST12and the step ST14.

In the sequence SQ, the step ST11 is first executed. In the step ST11, aplasma of a processing gas is generated in the processing chamber 12where the wafer W is accommodated. To do so, in the step ST11, theprocessing gas is supplied into the processing chamber 12 from a gassource selected among the gas sources of the gas source group 40. Thisprocessing gas used in the step ST11 includes a fluorocarbon gas. Theprocessing gas may further include a rare gas, e.g., Ar gas. In the stepST11, a pressure in the processing chamber 12 is set to a predeterminedlevel by the operation of the gas exhaust unit 50. In the step ST11, thehigh frequency power from the first high frequency power supply 62 issupplied to the lower electrode LE. Accordingly, the plasma of theprocessing gas including a fluorocarbon gas is generated and dissociatedfluorocarbon is deposited on the surface of the wafer W. As a result, adeposit DP is formed as shown in FIG. 8. The operation of each componentof the plasma processing apparatus 10 in the step ST11 can be controlledby the control unit Cnt.

Next, in the step ST12, the plasma of the processing gas is furthergenerated in the processing chamber 12 where the wafer W isaccommodated. To do so, in the step ST12, the processing gas is suppliedinto the processing chamber 12 from a gas source selected among the gassources of the gas source group 40. This processing gas used in the stepST12 includes a fluorocarbon gas. The processing gas may further includea rare gas, e.g., Ar gas. In the step ST12, a pressure in the processingchamber 12 is set to a predetermined level by the operation of the gasexhaust unit 50. In the step ST12, the high frequency power from thefirst high frequency power supply 62 is supplied to the lower electrodeLE. Accordingly, the plasma of the processing gas including thefluorocarbon gas is generated and dissociated fluorocarbon is depositedon the surface of the wafer W. As a result, the amount of the deposit DPis increased as shown in FIG. 9. The operation of each component of theplasma processing apparatus 10 in the step ST12 can be controlled by thecontrol unit Cnt.

As described above, in the step ST11 and the step ST12, the conditionthat realizes the deposition mode is selected. In this example, C₄F₆ gasis used as the fluorocarbon gas.

Moreover, the high frequency power for plasma generation used in thestep ST11 is set to be smaller than that used in the step ST12. When thehigh frequency power used for generation of the plasma of the processinggas including the fluorocarbon gas is small, the dissociation degree offluorocarbon is decreased and, thus, the amount of the deposit DP formedon the wafer W is also decreased. However, the etching amount of thewafer W is also decreased. On the other hand, when such a high frequencypower is large, the dissociation degree of fluorocarbon is increasedand, thus, the amount of the deposit DP formed on the wafer W isincreased. However, the etching amount of the wafer W is also increased.In the method MT, the high frequency power used in the step ST11 issmall as described above, so that the deposit DP can be thinly formed onthe second region R2 while suppressing the etching amount of the waferW, i.e., the etching amount of the second region R2. The amount of thedeposit PD formed on the wafer W can be increased by using the highfrequency power in the step ST12 while protecting the second region bythe thin deposit PD formed in the step ST11. Therefore, the amount ofthe deposit DP formed on the second region R2 can be increased whilesuppressing the etching of the second region R2. Especially, the etchingof the second region R2 can be suppressed by executing the steps ST11and ST12 in a period including a time when the second region R2 isexposed.

The step ST11 is executed under the following condition.

Pressure in processing chamber: 10 mTorr (1.33 Pa) to 50 mTorr (6.65 Pa)

Processing Gas

-   -   C₄F₆ gas: 2 sccm to 10 sccm    -   Ar gas: 500 sccm to 1500 sccm

High frequency power for plasma generation: 100 W to 300 W

High frequency bias power: 0 W

The step ST12 is executed under the following condition.

Pressure in processing chamber: 10 mTorr (1.33 Pa) to 50 mTorr (6.65 Pa)

Processing Gas

-   -   C₄F₆ gas: 2 sccm to 10 sccm    -   Ar gas: 500 sccm to 1500 sccm

High frequency power for plasma generation: 300 W to 1000 W

High frequency bias power: 0 W

Next, the step ST13 is executed in the present embodiment. In the stepST13, a plasma of a processing gas including an oxygen-containing gasand an inert gas is generated in the processing chamber 12. To do so, inthe step ST13, the processing gas is supplied into the processingchamber 12 from a gas source selected among the gas sources of the gassource group 40. In this example, this processing gas used in the stepST13 includes oxygen gas as the oxygen-containing gas. Further, in thisexample, the processing gas includes, as the inert gas, a rare gas suchas Ar gas. The inert gas may be nitrogen gas. In the step ST13, apressure in the processing chamber 12 is set to a predetermined level bythe operation of the gas exhaust unit 50. In the step ST13, the highfrequency power from the first high frequency power supply 62 issupplied to the lower electrode LE. In the step ST13, the high frequencybias power from the second high frequency power supply 64 may not besupplied to the lower electrode LE.

In the step ST13, active species of oxygen are generated and the amountof deposit DP on the wafer W is appropriately decreased by the activespecies of oxygen, as can be seen from FIG. 10. As a result, the openingMO and the upper opening UO are prevented from being blocked by anexcessive amount of deposit DP. In the case of the processing gas usedin the step ST13, the oxygen gas is diluted with the inert gas and,thus, excessive removal of the deposit DP can be suppressed. Theoperation of each component of the plasma processing apparatus 10 in thestep ST13 can be controlled by the control unit Cnt.

The step ST13 is executed under the following condition.

Pressure in processing chamber: 10 mTorr (1.33 Pa) to 50 mTorr (6.65 Pa)

Processing Gas

-   -   O₂ gas: 2 sccm to 20 sccm    -   Ar gas: 500 sccm to 1500 sccm

High frequency power for plasma generation: 100 W to 500 W

High frequency bias power: 0 W

In the present embodiment, the step ST13 in each sequence, i.e., asingle step ST13, is executed for two or more seconds. In the step ST13,the deposit DP can be etched at a rate of about 1 nm/sec or less. In thecase of executing the sequence by using the plasma processing apparatus10, it is required to switch gases when the steps ST12 to ST14 areshifted from one to another. Therefore, the step ST13 needs to beexecuted for two or more seconds in consideration of time required forstabilization of discharge. However, if the etching rate of the depositDP in the step ST13 is too high, the deposit for protecting the secondregion R2 may be excessively removed. Thus, the deposit DP is etched ata rate of about 1 nm/sec or less to suppress the excessive removal ofthe deposit DP in the step ST13. As a consequence, it is possible toappropriately control the amount of the deposit DP on the wafer W. Theetching rate of the deposit DP which is about 1 nm/sec or less in thestep ST13 can be realized by selecting a pressure in the processingchamber, a degree of dilution of oxygen in the processing gas with arare gas, i.e., an oxygen concentration, and a high frequency power forplasma generation from the above-described condition.

Next, in the step ST14, the first region R1 is etched. To do so, in thestep ST14, the processing gas is supplied into the processing chamber 12from a gas source selected among the gas sources of the gas source group40. This processing gas used in the step 14 includes an inert gas. Inthis example, the inert gas may be a rare gas such as Ar gas. Or, theinert gas may be nitrogen gas. In the step ST14, a pressure in theprocessing chamber 12 is set to a predetermined level by the operationof the gas exhaust unit 50. In the step ST14, the high frequency powerfrom the first high frequency power supply 62 is supplied to the lowerelectrode LE. In the step ST14, the high frequency bias power from thesecond high frequency power supply 64 is supplied to the lower electrodeLE.

The step ST14 is executed under the following condition.

Pressure in processing chamber: 10 mTorr (1.33 Pa) to 50 mTorr (6.65 Pa)

Processing Gas

-   -   Ar gas: 500 sccm to 1500 sccm

High frequency power for plasma generation: 100 W to 500 W

High frequency bias power: 20 W to 300 W

In the step ST14, a plasma of an inert gas is generated and ions areattracted to the wafer W. The first region R1 is etched by radicals offluorocarbon contained in the deposit DP. Accordingly, the first regionR1 in the recess formed by the second region R2 is etched and the loweropening LO is gradually formed, as can be seen from FIG. 11. Theoperation of each component of the plasma processing apparatus 10 in thestep ST14 can be controlled by the control unit Cnt.

In the present embodiment, the sequence SQ including the above-describedsteps ST11 to ST14 is repeated. As the sequence SQ is repeated, thedeposit DP is formed on the wafer W by the execution of the steps ST11and ST12 as can be seen from FIG. 12. Then, the amount of the deposit DPis decreased by the execution of the step ST13 as can be seen from FIG.13. Next, the first region R1 is further etched by the execution of thestep ST14 and, thus, the depth of the lower opening LO is increased, ascan be seen from FIG. 14. As the sequence SQ is further repeated, thedeposit DP is formed on the wafer W by the execution of the steps ST11and ST12, as can be seen from FIG. 15. Thereafter, the amount of thedeposit DP is decreased by the execution of the step ST13 as can be seenfrom FIG. 16. Next, the first region R1 is further etched by theexecution of the step ST14 and, thus, the depth of the lower opening LOis further increased, as can be seen from FIG. 17. Ultimately, the firstregion R1 is etched until the second region R2 is exposed at the bottomof the recess.

Referring back to FIG. 1, it is determined in the step STa of the methodMT whether or not a stop condition is satisfied. When the sequence SQhas been performed a predetermined number of times, it is determinedthat the stop condition is satisfied. When it is determined in the stepSTa that the stop condition is not satisfied, the sequence SQ isperformed again from the step ST11. On the other hand, when it isdetermined in the step STa that the stop condition is satisfied, theexecution of the method MT is terminated.

In the present embodiment, the conditions of the repeated sequences SQmay be set such that an etching amount of the first region R1 in thesequence SQ performed during a period including a time when the secondregion R2 is exposed (hereinafter, referred to as “first sequence”)becomes smaller than that of the first region R1 in a next sequence SQ(hereinafter, referred to as “second sequence”). In this example, theexecution time of the first sequence is set to be shorter than that ofthe second sequence. In this example, a ratio of the execution time ofthe steps ST11, ST12, ST13 and ST14 in the first sequence may be set tobe equal to that of the steps ST11, ST12, ST13 and ST14 in the secondsequence. For example, in the first sequence, the execution time of thestep ST11 is selected from a range of 2 sec to 5 sec; the execution timeof the step ST12 is selected from a range of 2 sec to 5 sec; theexecution time of the step ST13 is selected from a range of 2 sec to 5sec; and the execution time of the step ST14 is selected from a range of5 sec to 10 sec. In the second sequence, the execution time of the stepST11 is selected from a range of 2 sec to 10 sec; the execution time ofthe step ST12 is selected from a range of 2 sec to 10 sec; the executiontime of the step ST13 is selected from a range of 2 sec to 10 sec; andthe execution time of the step ST14 is selected from a range of 5 sec to10 sec.

Although the active species of fluorocarbon generated in the steps ST11and ST12 are deposited on the second region R2 and protect the secondregion R2, the second region R2 may be etched when the second region R2is exposed by the etching process of the first region R1. Therefore, inthe present embodiment, the first sequence is performed during a periodin which the second region R2 is exposed. Accordingly, the deposit DP isformed on the wafer W while decreasing the etching amount and the secondregion R2 is protected by the deposit DP. Then, the second sequence inwhich the etching amount is large is performed. As a result, in thepresent embodiment, the first region R1 can be etched while suppressingthe etching of the second region R2.

In the step ST14 of the sequence SQ (hereinafter, referred to as “thirdsequence”) executed after the second sequence, the high frequency biaspower may be set to be greater than the high frequency bias power usedin the step ST14 of the first sequence and the second sequence. Forexample, in the step ST14 of the first sequence and the second sequence,the high frequency bias power is set within a range from 20 W to 100 W.In the step ST14 of the third sequence, the high frequency bias power isset within a range from 100 W to 300 W. In the third sequence of thisexample, the execution time of the step ST11 is selected from a range of2 sec to 10 sec; the execution time of the step ST12 is selected from arange of 2 sec to 10 sec; the execution time of the step ST13 isselected from a range of 2 sec to 10 sec; and the execution time of thestep ST14 is selected from a range of 5 sec to 10 sec.

As can be seen from FIG. 15, the amount of the deposit DP on the wafer Wis considerably increased after the first sequence and the secondsequence. When the amount of the deposit DP is increased, the width ofthe opening MO, the width of the upper opening UO, and the width of thelower opening LO are decreased by the deposit DP. Accordingly, the flowvelocity of ions may not be enough to reach the deep portion of thelower opening LO. Since, however, a relatively large high frequency biaspower is used in the step ST14 of the third sequence, the energy of ionsattracted to the wafer W can be increased. As a result, even if thelower opening LO has a large depth, ions can reach the deep portion ofthe lower opening LO.

While various embodiments have been described, the disclosure may bevariously modified without being limited to the above-describedembodiments. For example, in the method MT, the high frequency power forplasma generation is supplied to the upper electrode 30. However, thehigh frequency power may be supplied to the lower electrode LE. Further,in the method MT, a plasma processing apparatus other than the plasmaprocessing apparatus 10 may be employed. Specifically, the method MT canbe performed by any plasma processing apparatus such as an inductivelycoupled plasma processing apparatus or a plasma processing apparatus forgenerating a plasma by using a surface wave such as a microwave.

The execution order of the steps ST11 to ST14 in the sequence SQ may bechanged. For example, in the sequence SQ, the step ST13 may be executedafter the step ST14.

A modified method may include only the sequence SQ. In that case, thewafer W is not limited to that shown in FIG. 2 and may be modified aslong as it includes a first region of silicon oxide and a second regionof silicon nitride.

It is not necessary that all of the repeatedly performed sequences SQinclude the step ST11. For example, the sequence SQ including the stepST11 may be performed during a period including a time when the secondregion R2 is exposed. The sequence SQ performed in other periods may notinclude the step ST11.

While the disclosure has been shown and described with respect to theembodiments, it will be understood by those skilled in the art thatvarious changes and modifications may be made without departing from thescope of the disclosure as defined in the following claims.

What is claimed is:
 1. An apparatus for etching a target object, thetarget object including a first silicon containing material and a secondsilicon containing material different from the first silicon containingmaterial, the apparatus comprising: a chamber having a gas inlet and agas outlet; a plasma generator; a controller configured to cause: (a)generating a first plasma from a processing gas with a first radiofrequency power, and exposing the target object to the first plasma toform a first deposit on the target object; (b) generating a secondplasma from the processing gas with a second radio frequency powergreater than the first radio frequency power, and exposing the targetobject to the second plasma to form a second deposit on the targetobject; and (c) generating a third plasma from an inert gas, andexposing the first deposit and the second deposit on the target objectto the third plasma to etch the first region.
 2. The apparatus of claim1, wherein the processing gas includes carbon species and fluorinespecies.
 3. The apparatus of claim 1, wherein the first deposit isthinner than the second deposit.
 4. The apparatus of claim 1, whereinthe target object is etched in (a) and (b) and an etching amount of thetarget object in (a) is smaller than an etching amount of the targetobject in (b).
 5. The apparatus of claim 1, wherein a sequence including(a) to (c) is repeatedly performed.
 6. The apparatus of claim 1, whereinthe controller is further configured to cause: (d) generating a forthplasma from an another processing gas, and exposing the target object tothe forth plasma to etch the first region before (a).
 7. The apparatusof claim 6, wherein each of the processing gas and the anotherprocessing gas includes carbon and fluorine, and wherein a ratio offluorine atoms to carbon atoms in the another processing gas used in (d)is higher than that in the processing gas used in (a) and (b).
 8. Theapparatus of claim 6, wherein (d) is performed with a bias power forattracting ions to the target object, and wherein the bias power used in(d) is greater than bias powers used in (a) and (b).
 9. The apparatus ofclaim 6, wherein the processing gas used in (a) and (b) includes C₄F₆gas, and wherein a ratio of fluorine atoms to carbon atoms in theanother processing gas used in (d) is higher than that in the C₄F₆ gas.10. The apparatus of claim 1, wherein the controller is furtherconfigured to cause: (e) generating a fifth plasma from anoxygen-containing gas and an inert gas, and exposing the target object.11. The apparatus of claim 10, wherein (e) is performed after (b). 12.The apparatus of claim 10, wherein (e) is performed before (c).
 13. Theapparatus of claim 1, wherein (c) is performed with a radio frequencybias power for attracting ions to the target object, and wherein theradio frequency bias power used in (c) is greater than radio frequencybias powers used in (a) and (b).
 14. The apparatus of claim 1, whereinthe second region is formed to have a recess, wherein the first regionfills the recess and covers the second region, wherein the target objectincludes a mask that is provided on the first region and has an openingprovided over the recess, and wherein the controller is furtherconfigured to cause: (f) generating a sixth plasma from anoxygen-containing gas, and exposing the target object to increase thewidth of the opening before (a).
 15. The apparatus of claim 1, whereinthe first silicon containing material is silicon oxide and the secondsilicon containing material is silicon nitride.
 16. The apparatus ofclaim 1, wherein the second region is formed to have a recess, whereinthe first region fills the recess and covers the second region, whereinthe target object includes a mask that is provided on the first regionand has an opening provided over the recess, and wherein the controllerconfigured to further cause: (g) etching the first region untilimmediately before the second region is exposed before (a).
 17. Theapparatus of claim 1, wherein (a) is executed in a period including atime when the second region is exposed.
 18. An apparatus for etching afirst silicon containing material with respect to a second siliconcontaining material different with the first silicon containingmaterial, the apparatus comprising: a chamber having a gas inlet and agas outlet; a plasma generator; a controller configured to cause: (a)generating a first plasma from a processing gas with a first radiofrequency power, and exposing a target object to the first plasma, thetarget object including the first silicon containing material and thesecond silicon containing material; (b) generating a second plasma fromthe processing gas with a second radio frequency power greater than thefirst radio frequency power, and exposing the target object to thesecond plasma; and (c) generating a third plasma from an inert gas; andexposing the target object to the third plasma.